This protocol investigates the role of glucocorticoids in suppression of TSH secretion during fasting. TSH levels will be compared between healthy subjects (who can increase cortisol levels in response to stress) and subjects with adrenal insufficiency given hydrocortisone (at physiologic, rather than stress, levels) during short-term caloric deprivation. TSH levels should be suppressed in the former group, but unaltered in the latter group.